The invention relates to an indicator device useful for measuring the level of a material stored in a tank.
In the manufacture of many industrial products, either solids or liquids, the product is temporarily stored in a tank before it is packaged or delivered to the user in some other form. A critical step in the manufacturing process is to be able to measure the amount of material in the tank at any given time. Conventional devices that may be used to measure the level of material in the tank include differential pressure (DP) cells, sonic devices, and plumb bobs. None of these devices are entirely satisfactory for measuring the level of a finely divided solid material inside a tank.
For example, it is very difficult to measure the level of finely divided solids, such as Methocel.RTM. cellulose ether, when the material is stored in a tank. If a DP cell is used, the fine material tends to blind or clog the diaphragm and interfere with the reading. Plumb bobs are not suitable devices for measuring the level of solids stored in a tank because the bob may tear loose from its line and damage the screw conveyer and rotary valves located in the product discharge lines. Sonic devices for measuring the level of a material also have certain drawbacks, in that they may give false levels, depending on particle size of the solids and the angle of repose of the surface. Also, when a tank is being filled with a particulate solid from an air stream, the dense cloud of "dust" within the tank can give false sonic data.
The present invention overcomes most of the problems described above. In one embodiment of the invention, telescoping tubular sections are raised and lowered within a tank containing a stored material by a winch unit that includes a cable string. A foot member at the bottom end of the telescoping assembly makes contact with the material in the tank and a counting and recording device measures and records the total distance traveled by the cable to indicate the level of material in the tank.